cmd/compile: arm64 build constraint not supported in bootstrapping ?

[shawndx]

What version of Go are you using (go version)?

$ go version
branch tip

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

go env Output

$ go env

arm64 platform

What did you do?

Add an arch-specific file, say nat_arm64.go, but it's not built during bootstrapping, leading to unexpected build error.

Command line of building the math/big packge:

/usr/lib/go-1.10/pkg/tool/linux_arm64/compile -o $WORK/b089/pkg.a -trimpath $WORK/b089 -p bootstrap/math/big -complete -buildid A-inRWtP3l76bAqzsiqn/A-inRWtP3l76bAqzsiqn -goversion go1.10.4 -D "" -importcfg $WORK/b089/importcfg -pack -c=4 ./accuracy_string.go ./arith.go ./arith_decl_pure.go ./decimal.go ./doc.go ./float.go ./floatconv.go ./floatmarsh.go ./ftoa.go ./int.go ./intconv.go ./intmarsh.go ./nat.go ./natconv.go ./prime.go ./rat.go ./ratconv.go ./ratmarsh.go ./roundingmode_string.go ./sqrt.go

Seems that build constraint for arm64 is not supported by go-1.10?
Tried with amd64 (nat_amd64.go), it works fine.

What did you expect to see?

bootstrapping build support arm64 build constraint, or any workaround solution.

What did you see instead?

build error in "Building Go toolchain1 using /usr/lib/go-1.10." as the arch-specific file is not included.

[shawndx]

As a comparison, command line of building math/big on amd64 where ./nat_amd64.go is included.

/home/xiaji01/util/go/pkg/tool/linux_amd64/compile -o $WORK/b097/pkg.a -trimpath "$WORK/b097=>" -p bootstrap/math/bi g -lang=go1.14 -complete -buildid SuQcvfNw1-wahpUcxV9E/SuQcvfNw1-wahpUcxV9E -D "" -importcfg $WORK/b097/importcfg -pac k -c=4 ./accuracy_string.go ./arith.go ./arith_decl_pure.go ./decimal.go ./doc.go ./float.go ./floatconv.go ./floatmar sh.go ./ftoa.go ./int.go ./intconv.go ./intmarsh.go ./nat.go ./nat_amd64.go ./natconv.go ./prime.go ./rat.go ./ratconv .go ./ratmarsh.go ./roundingmode_string.go ./sqrt.go

Thanks.

[bradfitz]

arm64 has been recognized since Go 1.5.

Please provide a complete repro.

[shawndx]

@bradfitz I got the following error with the enclosed change. Thanks a lot.

Building Go cmd/dist using /usr/lib/go-1.10. (go1.10.4 linux/arm64)
Building Go toolchain1 using /usr/lib/go-1.10.

bootstrap/math/big

/home/xiaji01/src/go.natsqr.arm/src/math/big/nat.go:271: undefined: karatsubaThreshold
/home/xiaji01/src/go.natsqr.arm/src/math/big/nat.go:423: undefined: karatsubaThreshold
/home/xiaji01/src/go.natsqr.arm/src/math/big/nat.go:436: undefined: karatsubaThreshold
/home/xiaji01/src/go.natsqr.arm/src/math/big/nat.go:520: undefined: karatsubaSqrThreshold
/home/xiaji01/src/go.natsqr.arm/src/math/big/nat.go:565: undefined: basicSqrThreshold
/home/xiaji01/src/go.natsqr.arm/src/math/big/nat.go:570: undefined: karatsubaSqrThreshold
/home/xiaji01/src/go.natsqr.arm/src/math/big/nat.go:581: undefined: karatsubaSqrThreshold
go tool dist: FAILED: /usr/lib/go-1.10/bin/go install -gcflags=-l -tags=math_big_pure_go compiler_bootstrap bootstrap/cmd/...: exit status 2

nat.patch.txt

[shawndx]

looks like *_arm64.go is excluded on arm64 platform, if I managed to bypass the error then toolchain1 recognizes them as expected.
(edit: the behavior is not specific to go-1.10)

[bradfitz]

Look at the command that failed; it includes tags=math_big_pure_go.

It's trying to build a non-assembly version first, and your patch deletes the pure Go definitions.

This is working as intended.

[shawndx]

Files with arm64 or wasm suffixes are ignored from bootstrapping build,

// cmd/dist/buildtool.go
112 // File suffixes that use build tags introduced since Go 1.4.
113 // These must not be copied into the bootstrap build directory.
114 var ignoreSuffixes = []string{
115 "_arm64.s",
116 "_arm64.go",
117 "_wasm.s",
118 "_wasm.go",
119 }

159 for _, suf := range ignoreSuffixes {
160 if strings.HasSuffix(name, suf) {
161 continue Dir
162 }
163 }

why are they ignored even they already have "// +build !math_big_pure_g"? Is it for supporting a GOROOT_BOOTSTRAP < Go 1.4? Thanks.

[ianlancetaylor]

The ignoreSuffixes list is because Go 1.4 didn't treat those suffixes specially. If we left them in the bootstrap directory it would break bootstrap with Go 1.4 which would try to compile those files when it shouldn't.

If it's important to make that work we could likely clean this up a bit by only ignoring the files if they have no build tags.

[bradfitz]

@ianlancetaylor, we could also add explicit +build tags to the copies in the bootstrap directory instead of skipping files.